1. Field of the Invention
The present invention relates to a wireless communication tag, which makes wireless communication with a reader/writer, and a wireless communication system using the wireless communication tag.
2. Description of the Related Art
Conventionally, a communication tag using an RFID tag, for example, is roughly divided into two types, i.e., an active type and a passive type, in view of the associated communication system. For the active type, a battery is loaded as a power supply source for activating the wireless communication tag. On the other hand, for the passive type, power is externally supplied for activating the wireless communication tag. The active-type communication tag is not only costly, but also requires battery discarding or replacement at cycle of several years because the battery must be loaded. On the other hand, the passive-type communication tag can achieve low cost and extended service life, and therefore, its expanded use is anticipated.
Three communication systems of the passive type are available which are represented by an electromagnetic coupling system, an electromagnetic induction system, and a radio wave system. These three systems are selectively used depending on a frequency for use. For example, a wireless communication tag 1 of the radio wave system is generally configured to have an RFIDIC chip 3 and a transmitting and receiving antenna 5, as shown in FIG. 2, and performs radio communication with a reader/writer (not shown). For example, a UHF band or a microwave band is utilized as a radio wave frequency band. Furthermore, a dipolar antenna 5 which forms an entire length of a half wavelength (λ/2) of a radio wave, for example, is utilized as the transmitting and receiving antenna 5.
In this case, the wireless communication tag 1 of the passive type is charged by receiving through the dipolar antenna 5 a radio wave (a readout radio wave) transmitted from the reader/writer. While the received radio wave is employed as power supply, the wireless communication tag 1 activates the IC chip 3, thereby communicating the ID (identification information) stored in the IC chip 3 to the reader/writer.
With the conventional wireless communication tag of the passive type as described above, a communication distance is undesirably limited according to the amount of power charge when the tag communicates the ID (identification information) with the reader/writer. Therefore, it has been necessary for this wireless communication tag to continuously receive a radio wave (a readout radio wave) transmitted from the reader/writer until an amount of power charge sufficient to make communication is obtained. Further, it has been necessary to ensure an electric field with enough intensity required for power charge. In view of the circumstances described above, Japanese Laid-open Patent Publication No. 2007-34951 proposes art of always supplying power for activating the wireless communication tag from a commercially available power supply, thereby ensuring the sufficient amount of power charge anytime and increasing a communication distance between the reader/writer and the wireless communication tag.
In the above-described art proposed in Japanese Laid-open Patent Publication No. 2007-34951, however, a configuration for connecting the commercially available power source must be additionally set up, thus resulting in a complicated wireless communication tag structure and high manufacturing cost. Furthermore, with this art, a condition for using the wireless communication tag is limited under an environment where the commercially available power source can be ensured, so that a certain limitation is undesirably imposed on an environment of using this wireless communication tag.
The present invention has been made in order to solve the above-described problems. It is an object of the present invention to provide a low-cost wireless communication tag and a wireless communication system, that ensure the sufficient amount of power charge regardless of a use environment to thereby increase a communication distance with the reader/writer.